The killings took place in the remote state of Jharkhand state earlier in the week.
Deputy police superintendent Animesh Nathani said the attackers were angered by a WhatsApp video warning local people a kidnapping gang was operating in the area.
"The incidents happened over two days in neighbouring districts which are populated by tribals," he said. "They lack awareness and took the WhatsApp video to be true."
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India's indigenous tribal communities have traditionally been at the bottom of the socioeconomic ladder, with some of the worst rates of poverty, malnutrition and life expectancy.
Child trafficking is a major problem in India, particularly in rural areas. Victims are sold off to work in factories or as prostitutes or beggars.
No arrests have yet been made over the latest killings. The Press Trust of India news agency said hundreds of local protesters had put up roadblocks to demand police action.
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